1. Field of Invention
This invention relates to heat exchange apparatus and method. The invention also relates to apparatus and method for improving the flow distribution of shell fluid in a shell and tube heat exchanger.
2. Description of the Prior Art
Heat transfer is an important part of many processes. As is well known, indirect transfer of heat from one medium to another is usually accomplished by the use of heat exchangers, of which there are many types such as for example double pipe, shell and tube, plate heat exchangers and the like. Although the art of heat exchanger design is highly developed, there remains room for improvement in a number of areas such as for example reducing pressure drop, increasing overall heat transfer coefficients, reducing fouling, and the like. In heat exchangers utilizing a tube bundle, such as shell and tube heat exchangers, improving fluid flow distribution as well as tube support are areas where room for improvement exists. The present invention is particularly concerned with improving the flow distribution and thus improving heat transfer efficiency of shell fluid in a shell and tube heat exchanger.
A shell and tube heat exchanger typically comprises a cylindrical shell, an approximately cylindrical bundle of tubes longitudinally disposed within the shell, means for supporting the tubes in the shell, inlet and outlet means for introducing a first fluid to and withdrawing the first fluid from the tubes, and inlet and outlet means for introducing a second fluid to and withdrawing the second fluid from the interior of the shell. Indirect heat exchange between the first and second fluids is effected by passing one fluid through the tubes while passing the other fluid through the shell, wherein the first and second fluids can be passed through the tubes and shell in either concurrent or countercurrent flow relation. For purposes of nomenclature, the fluid that passes through the tubes is referred to herein as the tube fluid. Similarly, the fluid that passes through the shell is referred to herein as the shell fluid. The flow path of the shell fluid is referred to herein as the normal flow path.
The art has heretofore recognized the need to maximize the area of contact between the flowing shell fluid and the tubes in order to maximize heat exchange efficiency. Because of the low pressure drop and lack of resistance to flow along the path between the inlet and outlet of the shell side of the heat exchanger, the flowing shell fluid substantially by-passes areas near the shell fluid inlet and outlet. This channeling of flow adversely affects heat exchange efficiency. The areas of the heat exchanger apparatus which are by-passed when fluid flows along the normal flow path are referred to herein as the normally by-passed areas, as illustrated by areas 3 and 4 in FIG. 1.
In FIG. 1, the shell of a typical shell and tube heat exchanger is indicated by the numeral 1. For simplicity, the tubes and rod baffles are not shown. It is assumed that the rod baffles are evenly distributed across the shell and that the number of rods employed in each baffle is approximately the seam. The normal flow path 2 of shell fluid through the heat exchanger tends to channel and by-pass the normally by-passed areas designated 3 and 4. As a result, the portions of those tubes passing through normally by-passed areas 3 and 4 are not in good contact with the flowing shell fluid. Accordingly, it is desired to divert shell fluid flow to the normally by-passed areas 3 and 4 in order to increase overall heat exchange efficiency.